When an optic element of for example a laser diode or photo diode is coupled to a optic fiber, an wave guide of the optic element must be aligned with a core of the optic fiber with a precision of .+-.1 .mu.m in the horizontal direction and .+-.1.0 .mu.m in the vertical direction to transmit light emitted from the optic element to the optic fiber without loss.
An optic fiber-optic element coupling device has been used in the prior art in which used a V-shape groove for mounting the optic fiber and a solder bump for flip chip bonding the optic element is formed so as to align the optic element with the optic fiber precisely.
A method for self-aligning a optic fiber with a optic element using the optic fiber-optic element coupling device mentioned above is disclosed in IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, VOL. 13, NO. 4, pp. 780-786, DECEMBER(1990).
The optic fiber is mounted on a silicon substrate having a V-shape groove capable of being dimension controlled precisely and then the optic element is flip chip bonded using a solder bump to align the wave guide with the core of the optic fiber by the method described in the above documents.
This method has a good optic coupling efficiency and a superior electric and thermal property that is better than existing wire bonding technology because the wave guide of the optic element is aligned with the core of the optic fiber having a small error of .+-.1 .mu.m both in the horizontal and vertical direction.
And in the optic element-optic fiber coupling device for self-aligning the optic element with the optic fiber, metal pads are formed by vacuum evaporation process and a photolithography technology on a predetermined portion of the top surface of a silicon substrate having an insulating film formed on the surface thereof and a V-shape groove is formed by an anisotropic etching method.
And, an insulating film is formed and partially removed to expose a predetermined portion on which solder bumps are formed on the metal pads.
However when the steps at forming the V-shape groove and exposing the metal pads to form the solder bump is performed by different processes using different mask, there is alignment error between the V-shape groove and the solder bumps, especially when the V-shape groove has a large width and a depth, the alignment error increases, and the coupling efficiency between the optic element and the optic fiber deteriorates.